1. Field of the Invention
The present invention relates generally to eyeglass lenses. More particularly, the invention relates to a lens forming composition, system and method for making photochromic, ultraviolet/visible light absorbing, and colored plastic lenses by curing the lens forming composition using activating light.
2. Description of the Relevant Art
It is conventional in the art to produce optical lenses by thermal curing techniques from the polymer of diethylene glycol bis(allyl)-carbonate (DEG-BAC). In addition, optical lenses may also be made using ultraviolet (xe2x80x9cUVxe2x80x9d) light curing techniques. See, for example, U.S. Pat. No. 4,728,469 to Lipscomb et al., U.S. Pat. No. 4,879,318 to Lipscomb et al., U.S. Pat. No. 5,364,256 to Lipscomb et al., U.S. Pat. No. 5,415,816 to Buazza et al., U.S. Pat. No. 5,529,728 to Buazza et al., U.S. Pat. No. 5,514,214 to Joel et al., U.S. Pat. No. 5,516,468 to Lipscomb, et al., U.S. Pat. No. 5,529,728 to Buazza et al., U.S. Pat. No. 5,689,324 to Lossman et al., and U.S. patent application Ser. No. 07/425,371 filed Oct. 26, 1989, Ser. No. 08/439,691 filed May 12, 1995, Ser. No. 08/454,523 filed May 30, 1995, Ser. No. 08/453,770 filed May 30, 1995, Ser. No. 08/636,510 filed Apr. 19, 1996, Ser. No. 08/663,703 filed Jun. 14, 1996, Ser. No. 08/666,062 filed Jun. 14, 1996, Ser. No. 08/853,134 filed May 8, 1997, Ser. No. 08/844,557 filed Apr. 18, 1997, Ser. No. 08/904,289 filed Jul. 31, 1997, and Ser. No. 08/959,973 filed Oct. 29, 1997, all of which are hereby specifically incorporated by reference.
Curing of a lens by ultraviolet light tends to present certain problems that must be overcome to produce a viable lens. Such problems include yellowing of the lens, cracking of the lens or mold, optical distortions in the lens, and premature release of the lens from the mold. In addition, many of the useful ultraviolet light-curable lens forming compositions exhibit certain characteristics that increase the difficulty of a lens curing process. For example, due to the relatively rapid nature of ultraviolet light initiated reactions, it is a challenge to provide a composition that is ultraviolet light curable to form an eyeglass lens. Excessive exothermic heat tends to cause defects in the cured lens. To avoid such defects, the level of photoinitiator may be reduced to levels below what is customarily employed in the ultraviolet curing art.
While reducing the level of photoinitiator addresses some problems, it may also cause others. For instance, lowered levels of photoinitiator may cause the material in regions near an edge of the lens and proximate a gasket wall in a mold cavity to incompletely cure due to the presence of oxygen in these regions (oxygen is believed to inhibit curing of many lens forming compositions or materials). Uncured lens forming composition tends to result in lenses with xe2x80x9cwetxe2x80x9d edges covered by sticky uncured lens forming composition. Furthermore, uncured lens forming composition may migrate to and contaminate the optical surfaces of the lens upon demolding. The contaminated lens is then often unusable.
Uncured lens forming composition has been addressed by a variety of methods (see, e.g., the methods described in U.S. Pat. No. 5,529,728 to Buazza et al). Such methods may include removing the gasket and applying either an oxygen barrier or a photoinitiator enriched liquid to the exposed edge of the lens, and then re-irradiating the lens with a dosage of ultraviolet light sufficient to completely dry the edge of the lens prior to demolding. During such irradiation, however, higher than desirable levels of irradiation, or longer than desirable periods of irradiation, may be required. The additional ultraviolet irradiation may in some circumstances cause defects such as yellowing in the lens.
The low photoinitiator levels utilized in many ultraviolet curable lens forming compositions may produce a lens that, while fully-cured as measured by percentage of remaining double bonds, may not possess sufficient cross-link density on the lens surface to provide desirable dye absorption characteristics during the tinting process.
Various methods of increasing the surface density of such ultraviolet light curable lenses are described in U.S. Pat. No. 5,529,728 to Buazza et al. In one method, the lens is de-molded and then the surfaces of the lens are exposed directly to ultraviolet light. The relatively short wavelengths (around 254 nm) provided by some ultraviolet light sources (e.g., a mercury vapor lamp) tend to cause the material to cross-link quite rapidly. An undesirable effect of this method, however, is that the lens tends to yellow as a result of such exposure. Further, any contaminants on the surface of the lens that are exposed to short wavelengths of high intensity ultraviolet light may cause tint defects.
Another method involves exposing the lens to relatively high intensity ultraviolet radiation while it is still within a mold cavity formed between glass molds. The glass molds tend to absorb the more effective short wavelengths, while transmitting wavelengths of about 365 nm. This method generally requires long exposure times and often the infrared radiation absorbed by the lens mold assembly will cause premature release of the lens from a mold member. The lens mold assembly may be heated prior to exposure to high intensity ultraviolet light, thereby reducing the amount of radiation necessary to attain a desired level of cross-link density. This method, however, is also associated with a higher rate of premature release.
It is well known in the art that a lens mold/gasket assembly may be heated to cure the lens forming composition from a liquid monomer to a solid polymer. It is also well known that such a lens may be thermally postcured by applying convective heat to the lens after the molds and gaskets have been removed from the lens.
In this application the terms xe2x80x9clens forming materialxe2x80x9d and xe2x80x9clens forming compositionsxe2x80x9d are used interchangeably.
An embodiment of an apparatus for preparing an eyeglass lens is described. The apparatus includes a coating unit and a lens curing unit. The coating unit may be configured to coat either mold members or lenses. Preferably, the coating unit is a spin coating unit. The lens curing unit may be configured to direct activating light toward mold members. The mold members are part of a mold assembly that may be placed within the lens curing unit. Depending on the type of lens forming composition used, the apparatus may be used to form photochromic and non-photochromic lenses. The apparatus is preferably configured to allow the operation of both the coating unit and the lens curing unit substantially simultaneously.
The coating unit is preferably a spin coating unit. The spin coating unit preferably comprises a holder for holding an eyeglass lens or a mold member. The holder is preferably coupled to a motor that is preferably configured to rotate the holder. An activating light source may be incorporated into a cover. The cover may be drawn over the body of the lens curing unit, covering the coating units. The activating light source is preferably positioned, when the cover is closed, such that activating light may be applied to the mold member or lens positioned within the coating unit. An activating light source may be an ultraviolet light source, an actinic light source (e.g., a light source producing light having a wavelength between about 380 nm to 490 nm), a visible light source and/or an infra-red light source. Preferably, the activating light source is an ultraviolet light source.
The lens curing unit includes at least one, preferably two activating light sources for irradiating a mold assembly. Mold assembly holders may be positionable within the lens forming apparatus such that the activating light may be applied to the mold member during use. A filter is preferably positioned between the mold assemblies and the activating light source. The filter is preferably configured to manipulate the intensity of activating light that is directed toward the mold members. The filter may be a hazy filter that includes a frosted glass member. Alternatively, the filter may be a liquid crystal display (xe2x80x9cLCDxe2x80x9d) panel.
An LCD panel for use as a filter is preferably a monochrome trans-flective panel with the back light and reflector removed. The intensity of the light is preferably reduced as the light passes through the LCD panel. The LCD panel is preferably programmable such that the light transmissibility of the LCD panel may be altered. In use, a predetermined pattern of light and dark regions may be displayed on the LCD panel to alter the intensity of light passing through the panel. One advantage of an LCD panel filter is that a pattern may be altered during a curing cycle. For example, the pattern of light and dark regions may be manipulated such that a lens is initially cured from the center of the lens, then the curing may be gradually expanded to the outer edges of the lens. This type of curing pattern may allow a more uniformly cured lens to be formed.
Another advantage is that the LCD panel may be used as a partial shutter to reduce the intensity of light reaching the mold assembly. By blackening the entire LCD panel the amount of light reaching any portion of the mold assembly may be reduced. In this manner, the LCD may be used to create xe2x80x9cpulsesxe2x80x9d of light by alternating between a transmissive and darkened mode.
In another embodiment, an LCD panel may be used to allow different patterns and/or intensities of light to reach two separate mold assemblies. If the mold assemblies are being used to create lenses having significantly different powers, each mold assembly may require a significantly different light irradiation pattern and/or intensity. The use of an LCD filter may allow the irradiation of each of the mold assemblies to be controlled individually.
When non-LCD type filters are used, it may be necessary to maintain a library of filters for use in the production of different types of prescription lenses. Typically, each individual prescription will need a particular filter pattern to obtain a high quality lens. Since an LCD panel is programmable in a variety of patterns, it is believed that one may use a single LCD panel, rather than a library of filters. The LCD panel may be programmed to fit the needs of the specific type of lens being formed.
The LCD panel filters may be coupled to a programmable logic device that may be used to design and store patterns for use during curing. FIG. 7-10 show a number of patterns that may be generated on an LCD panel and used to filter activating light. Each of these patterns is preferably used for the production of a lens having a specific prescription power.
The lens forming apparatus may include a post-cure unit. The post-cure unit is preferably configured to apply heat and activating light to mold assemblies or lenses disposed within the post-cure unit.
The lens forming apparatus may also include a programmable controller configured to substantially simultaneously control the operation of the coating unit, the lens curing unit and the post-cure unit. The apparatus may include a number of light probes and temperature probes disposed within the coating unit, lens curing unit, and the post-cure unit. These probes preferably relay information about the operation of the individual units to the controller. The information relayed may be used to control the operation of the individual units. The operation of each of the units may also be controlled based on the prescription of the lens being formed.
The controller may be configured to control various operations of the coating unit. For example, when a spin coating unit is used the controller may control the rotation of the lens or mold member during a coating process (e.g., whether the lens or mold members are rotated or not and/or the speed of rotation) and the operation of the coating unit lamps (e.g., whether the lamps are on or off and/or the time the lamps are on).
The controller may also be configured to control the various operations of the lens curing unit. Some of the operations that may be controlled or measured by the controller include: (i) measuring the ambient room temperature; (ii) determining the dose of light (or initial dose of light in pulsed curing applications) required to cure the lens forming composition, based on the ambient room temperature; (iii) applying the activating light with an intensity and duration sufficient to equal the determined dose; (iv) measuring the composition""s temperature response during and subsequent to the application of the dose of light; (v) calculating the dose required for the next application of activating light (in pulsed curing applications); (vi) applying the activating light with an intensity and duration sufficient to equal the determined second dose; (vii) determining when the curing process is complete by monitoring the temperature response of the lens forming composition during the application of activating light; (viii) turning the upper and lower light sources on and off independently; (ix) monitoring the lamp temperature, and controlling the temperature of the lamps by activating cooling fans proximate the lamps; and (x) turning the fans on/off or controlling the flow rate of an air stream produced by a fan to control the composition temperature;
The controller may also be configured to control the operation of the post-cure unit. Some of the operations that may be controlled include control of the operation of the lamps (e.g., whether the lamps are on or off and the time the lamps are on); and operation of the heating device (e.g., whether the heating unit is turned on or off and/or the amount of heat produced by the heating device).
Additionally, the controller provides system diagnostics and information to the operator of the apparatus. The controller may notify the user when routine maintenance is due or when a system error is detected. The controller may also manage an interlock system for safety and energy conservation purposes. The controller may prevent the lamps from operating when the operator may be exposed to light from the lamps.
The controller may also be configured to interact with the operator. The controller preferably includes an input device and a display screen. A number of operations controlled by the controller, as described above, may be dependent on the input of the operator. The controller may prepare a sequence of instructions based on the type of lens (clear, ultraviolet/visible light absorbing, photochromic, colored, etc.), prescription, and type of coatings (e.g., scratch resistant, adhesion promoting, or tint) inputted by an operator.
A variety of lens forming compositions may be cured to form a plastic eyeglass lens in the above described apparatus. Colored lenses, photochromic lenses, and ultraviolet/visible light absorbing colorless lenses may be formed. The lens forming compositions may be formulated such that the conditions for forming the lens (e.g., curing conditions and post cure conditions) may be similar without regard to the lens being formed. In an embodiment, a clear lens may be formed under similar conditions used to form photochromic lenses by adding a colorless, non-photochromic ultraviolet/visible light absorbing compound to the lens forming composition. The curing process for forming a photochromic lens is such that higher doses of activating light than are typically used for the formation of a clear, non-ultraviolet/visible light absorbing lens may be required. In an embodiment, ultraviolet/visible light absorbing compounds may be added to a lens forming composition to produce a substantially clear lens under the more intense dosing requirements used to form photochromic lenses. The ultraviolet/visible light absorbing compounds may take the place of the photochromic compounds, making curing at higher doses possible for clear lenses. An advantage of adding the ultraviolet/visible light absorbers to the lens forming composition is that the clear lens formed may offer better protection against ultraviolet/visible light rays than a clear lens formed without such compounds.
An embodiment relates to an improved gasket for engaging a mold. The gasket is preferably configured to engage a first mold set for forming a first lens of a first power. The gasket preferably includes at least four discrete projections for spacing mold members of a mold set. The projections are preferably arranged on an interior surface of the gasket. The projections are preferably evenly spaced around the interior surface of the gasket; in a preferred embodiment, the spacing between each projection is about 90 degrees.
In another embodiment, an improved gasket includes a fill port for receiving a lens forming composition while fully engaged to a mold set. The fill port preferably extends from an interior surface of the gasket to an exterior surface of the gasket. Consequently, the gasket need not be partially disengaged from a mold member of a mold set in order to receive a lens forming composition.
In another embodiment, a mold/gasket assembly for making plastic prescription lenses preferably includes a first mold set for forming a first lens of a first power and a gasket for engaging the first mold set. The first mold set may contain a front mold member and a back mold member. The back mold member is also known as the convex mold member. The back mold member preferably defines the concave surface of a convex lens. The gasket is preferably characterized by at least four discrete projections for spacing the front mold member from the back mold member. A mold cavity for retaining a lens forming composition is preferably at least partially defined by the front mold member, the back mold member, and the gasket. The back mold member preferably has a steep axis and a flat axis. Each of the projections preferably forms an oblique angle with the steep and the flat axis of the mold members. In a preferred embodiment, these angles may each be about 45 degrees. Since the gasket does not include a continuous lip along its interior surface for spacing mold members, as is conventional in the art, the gasket may be configured to engage a large variety of mold sets. For example, the gasket may be configured to engage a second mold set for forming a second lens of a second power.
In another embodiment, a mold/gasket assembly for making plastic prescription lenses includes a mold set for forming a lens and a gasket configured to engage the mold set. The gasket is preferably characterized by a fill port for receiving a lens forming composition while the gasket is fully engaged to the mold. The fill port preferably extends from an interior surface to an exterior surface of the gasket. The mold set preferably contains at least a front mold member and a back mold member. A mold cavity for retaining a lens forming composition is preferably at least partially defined by the front mold member, the back mold member, and the gasket.
A method for making a plastic eyeglass lens is described. The method preferably includes engaging a gasket with a first mold set for forming a first lens of a first power. The first mold set preferably contains at least a front mold member and a back mold member. A mold cavity for retaining a lens forming composition may be at least partially defined by the front mold member, the back mold member, and the gasket. The gasket is preferably characterized by at least four discrete projections arranged on an interior surface thereof for spacing the front and back mold members. Engaging the gasket with the mold set preferably includes positioning the back mold members such that each of the projections forms an oblique angle with the steep and flat axis of the back mold member. In a preferred embodiment, this angle is about 45 degrees. The method preferably further includes introducing a lens forming composition into the mold cavity and curing the lens forming composition.
An additional embodiment provides a method for making a plastic eyeglass lens. The method preferably includes engaging a gasket with a first mold set for forming a first lens of a first power. The first mold set preferably contains at least a front mold member and a back mold member. A mold cavity for retaining a lens forming composition may be at least partially defined by the front mold member, the back mold member, and the gasket. Preferably, the method further includes introducing a lens forming composition through a fill port, wherein the front and back mold members remain fully engaged with the gasket during the introduction of the lens forming composition. The lens forming composition may then be cured.
In an embodiment, a composition that includes two or more photochromic compounds may further include a light effector composition to produce a lens that exhibits an activated color that differs from an activated color produced by the photochromic compounds without the light effector composition. The activated color is defined as the color a lens achieves when exposed to a photochromic activating light source (e.g., sunlight). A photochromic activating light source is defined as any light source that produces light having a wavelength that causes a photochromic compound to become colored. Photochromic activating light is defined as light that has a wavelength capable of causing a photochromic compound to become colored. The photochromic activating wavelength band is defined as the region of light that has a wavelength that causes coloring of photochromic compounds. The light effector composition may include any compound that exhibits absorbance of at least a portion of the photochromic activating wavelength band. Light effector compositions may include photoinitiators, ultraviolet/visible light absorbers, ultraviolet light stabilizers, and dyes. In this manner, the activated color of a lens may be altered without altering the ratio and or composition of the photochromic compounds. By using a light effector composition, a single lens forming composition may be used as a base solution to which a light effector may be added in order to alter the activated color of the formed lens.
The addition of a light effector composition that absorbs photochromic activating light may cause a change in the activated color of the formed lens. The change in activated color may be dependent on the range of photochromic activating light absorbed by the light effector composition. The use of different light effector compositions may allow an operator to produce photochromic lenses with a wide variety of activated colors (e.g., red, orange, yellow, green, blue, indigo, violet, gray, or brown).
In an embodiment, an ophthalmic eyeglass lens may be made from an activating light curable lens forming composition comprising a monomer composition and a photoinitiator composition. The monomer composition preferably includes a polyethylenic functional monomer. Preferably, the polyethylenic functional monomer composition includes an aromatic containing polyether polyethylenic functional monomer. In one embodiment, the polyethylenic functional monomer is preferably an ethoxylated bisphenol A di(meth)acrylate.
The monomer composition may include additional monomers to modify the properties of the formed eyeglass lens and/or the lens forming composition. Monomers which may be used in the monomer composition include polyethylenic functional monomers containing groups selected from acrylyl or methacrylyl.
In one embodiment, the photoinitiator composition preferably includes bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylphenyl)phosphine oxide, commercially available from Ciba Additives in Tarrytown, N.Y. under the trade name of Irgacure 819. In another embodiment, the photoinitiator composition may include a mixture of photoinitiators. Preferably, a mixture of Irgacure 819 and 1-hydroxycyclohexylphenyl ketone, commercially available from Ciba Additives under the trade name of Irgacure 184, is used.
In another embodiment, an ophthalmic eyeglass lens may be made from an activating light curable lens forming composition comprising a monomer composition, a photoinitiator composition and a co-initiator composition. An activating light absorbing compound may also be present. An activating light absorbing compound is herein defined as a compound which absorbs at least a portion of the activating light. The monomer composition preferably includes a polyethylenic functional monomer. Preferably, the polyethylenic functional monomer is an aromatic containing polyether polyethylenic functional monomer. In one embodiment, the polyethylenic functional monomer is preferably an ethoxylated bisphenol A di(meth)acrylate.
The co-initiator composition preferably includes amine co-initiators. Preferably, acrylyl amines are included in the co-initiator composition. In one embodiment, the co-initiator composition preferably includes a mixture of CN-384 and CN-386.
Examples of activating light absorbing compounds includes photochromic compounds, UV stabilizers, UV absorbers, and/or dyes.